Keyer circuit



April 19, 1966 A. MILHO 3,247,306

KEYER CIRCUIT Filed Dec. 5, 1962 INVENTOR:

mzm ww United States Patent 3,247,306 KEYER CIRCUIT Alexander Milho,Chicago, Ill., assignor to Hammond Organ Company, Chicago, 11]., acorporation of Delaware Filed Dec. 3, 1962., Ser. No. 241,999 4 Claims.(Cl. 841.13)

The present invention relates in general to a percussion sustain keyerfor use in electrical musical instruments. More particularly, it relatesto keyer circuits for organs of the type having free-running oscillatorsas opposed to systems which turn the individual oscillators on and offby operation of key contacts. The keyers provide the keyed signal with afull percussive envelope which is independent for each keyed tone signalsource and automatic in its operation and in which the percussionsustain effect is achieved by a single key contact for each playing key.

Usual percussion circuits for electrical musical instru- 'ments are ofseveral different types. In one type, operation of a playing key permitsthe note to sound percussively and thereafter it decays during a sustainperiod while the key is held operated. If the key is released before thepercussion envelope is complete, the tone generator is cut off and thesignal immediately ceases, furthermore release of the key during the sustain period may have other deleterious effects upon the tone signal. Inanother type of percussion circuit, the tone is sounded at a constantlevel while the key is held operated and after the key is released, thetone is sustained on a declining basis for a short period of time. Bothtypes of percussion therefore have disadvantages which have heretoforebeen difiicult to remedy since in one case the time of key operation isvariable and therefore the percussion effect is interrupted, while inthe other the tone is given a sustain period only on release of the key.

In addition, many percussion circuits employ complex contactarrangements for each organ key due to the need to place differingpotentials across the key contacts at the various organ keys. Thepresent invention simplifies the percussion key contact structure byenabling the use of a common bus configuration in the keyboard.

One object of the invention is to provide a novel keyer circuit forproviding sustained type percussion in which the percussive envelope isnever suddenly interrupted by release of a key.

The above and other objects of the present invention will becomeapparent on examination of the following specification and claimstogether with the drawing.

In the drawing a percussion keyer circuit for use in an electrical organis indicated generally by the reference character 10. It comprises atransistor 12 of the PNP type having an emitter circuit 14, a collectorcircuit 16 and a base circuit 18.

The collector circuit 16 is connected through the pri mary 20 of anoutput transformer T1 to a source of negative potential. A lead 22connects the primary 20 to a similar collector circuit of each of aplurality of other keyers which feed the transformer T1. The output ofthe transformer T1 is applied through a suitable output system to a loudspeaker or similar transducer.

A resistor R1 is connected across the secondary of transformer T1 whichacts as a mixer and provides a voltage gain, while a low frequencytransient filter comprising capacitors C1, C2 and C3 and inductance L1serves to filter the output of transformer T1. A resistor R2 is alsoconnected across the output of transformer T1.

The emitter circuit 14 of transistor 12 is also con "ice nected througha low frequency transient filter compris ing resistors R3 and R4 and acapacitor C4 to a tone signal source 22 to ground. A similar signalsource is provided for the other keyers feeding transformer T1 over lead22.

The base circuit 18 of the transistor 12 is connected through a resistorR5 to a source 24 of approximately one volt positive potential. The basecircuit is also connected to a large capacitor C5 and to one terminal ofa diode D1 poled to pass current when the base circuit is positive withrespect to the other terminal of diode D1.

The other terminal of diode D1 is connected to a diode D2 poled in thereverse direction and connected in shunt with capacitor C5. Diode D1 isalso connected through series connected resistors R6 and R7 and througha diode D3 poled in the same direction as diode D1 to ground. Thejunction of resistors R6 and R7 is connected to ground through acapacitor C6 and the junction of resistor R7 and diode D3 is connectedto one terminal of a keying capacitor C7.

The other terminal of capacitor C7 is connected through a resistor R8 toa source 26 of about six volts positive potential so that capacitor C7is normally charged to this value. One playing key 28 of the organ isadapted, when operated, to connect the junction of resistor R8 andcapacitor C7 to ground.

Normally then, with the key 28 open as shown, the capacitor C7 ischarged to a value of +6 volts through the resistor R8. The base circuit18 of the transistor has a potential established *by the voltage dropacross resistor R5 as current flows from the +1 volt battery source 24through the diode D1 and the resistors R6 and R7 through the diode D3 toground. This potential is such that the transistor is normallynonconductive and no signal from the source 22 appears across the outputtransformer T1.

In response to the closure of the key 28 as the organ is played,capacitor C7 has one side connected to ground potential so that anegative pulse appears across resistors R7 and R6 and the capacitor C5.The diode D3 blocks the negative pulse and the capacitor C5 partiallydischarges through resistors R6 and R7 to render the base circuit 18 ofthe transistor 12 slightly negative. The

transistor 12 therefore becomes conductive to immediate-.

ly pass the signal provided from the tone source 22 to the outputtransformer T1 and the output system. The capacitor C6 and resistors R6and R7 filter any transient resulting contact bounce at key 28.

After the initial negative pulse from capacitor C7, capacitor C5potential returns toward the normal base potential at a desired ratedependent on the circuit time constants and cuts off the transistor 12irrespective of the length of time key 28 is held operated.

When the key 28 is opened, of course, the capacitor C7 charges positive.The diode D3 blocks this charge from the base circuit of the transistorand the keyer circuit 10 assumes its normal condition. Thus,irrespective of whether the key 28 is operated momentarily or for anextended duration the percussive effect provided to the tone from source22 is completed, since release of the key does not open a set ofcontacts in the tone generator output circuit as is customary ofpercussion circuits of the type which supply a percussive envelope eventhough a key is continuously held. The other keyers connected totransformer T1 may of course be arranged to provide similar or differentpercussive effects, as desired, but they too are arranged topercussively key the signal Without the need for key contacts in thegenerator output circuits.

Although the foregoing describes one embodiment of the invention, it isbelieved capable of numerous adaptations, wherefore the limitations ofthe invention are believed more adequately set forth in the accompanyingclaims.

I claim:

1. In an individual percussion keyer circuit for a musical instrumentfor use with a respective individual musical tone signal sourcerepresentative of a single musical note to connect the respective sourceto an output system common to a plurality of independent such sourcesupon the actuation of a respective playing key, an electronic variableimpedance device the impedance of which is dependent upon the potentialapplied to a terminal thereof, circuit means including said variableimpedance device for connecting said source to said output system, meansnormally applying a bias potential to said terminal to render saidcircuit means ineffective to conduct said signal to said output system,means including the playing key for applying a pulse to said variableimpedance device terminal in response to actuation of said key to changethe potential at said terminal substantially instantaneously to rendersaid circuit means effective to conduct said signal to said out-putsystem, and automatic means operative with the application of said pulseto reestablish said normal bias potential to said terminal at a slowrate followingthe application of said pulse to said terminal forprogressively rendering said circuit means ineffective to conduct saidsignal to said output system.

2. In an individual percussion keyer circuit for a musical instrumentfor use with a respective individual musical tone signal sourcerepresentative of a single musical note to connect the respective sourceto an output system common to a plurality of independent such sourcesupon the actuation of a respective playing key, an electronic variableimpedance device the impedance of which is dependent upon the potentialapplied to a terminal thereof, circuit means including said variableimpedance device for connecting said source to said output system, meansincluding the playing key for applying a pulse to said variableimpedance device terminal in response to actuation of said key to changethe potential at said terminal substantially instantaneously to rendersaid circuit means effective to conduct said signal to said outputsystem, automatic means operative with the application of said pulse toreestablish said normal bias potential to said terminal at a slow ratefollowing the application of said pulse to said terminal forprogressively rendering said circuit means ineffective to conduct saidsignal to said output system, said pulse applying means comprising acapacitor, means including a potential source and an impedance elementfor applying a potential to one side of said capacitor, means includingsaid playing key for suddenly removing the last said potential from saidone side of said capacitor when said playing key is actuated, circuitmeans for connecting the other side of said capacitor to said terminal,the last said circuit means including an impedance element and aunidirectional element polarized to conduct when said other side of saidcapacitor has a potential that will cause said circuit means includingsaid variable impedance device to conduct when the last said potentialis applied to said terminal, a charge removing circuit including, aunidirectional element connected to v said other side of said capacitor,and the last said unidireccal instrument for use with a respectiveindividual musical tone signal source representative of a single musicalnote to connect the respective source to an output system common to aplurality of independent such sources upon the actuation of a respectiveplaying key, an electronic variable impedance device the impedance ofwhich is dependcut upon the potential applied to a terminal thereof,circuit means including said variable impedance device for connectingsaid source to said output system, means normally applying a positivebias potential to said terminal to render said circuit means ineffectiveto conduct said signal to said output system, means including a playingkey for applying a negative pulse to said variable impedance deviceterminal in response to actuation of said key to lower the potential atsaid terminal substantially instantaneously to render said circuit meanseflfective to conduct said signal to said output system, automatic meansoperative with the application of said pulse to reestablish said normalbias potential to said terminal at a slow rate following the applicationof said pulse to said terminal for progressively rendering said circuitmeans inefie'ctive to conduct said signal to said output system, saidmeans for supplying said pulse to said variable impedance deviceterminal comprising a capacitor, circuit means including a source ofpositive potential and an impedance element connected for applying apositive potential to one side of said capacitor, a circuit includingsaid playing key for suddenly removing said potential from said one sideof said capacitor when said playing key is actuated, circuit means forconnecting the other side of said capacitor to said terminal, the lastsaid circuit means including an impedance element and a unidirectionalelement polarized to conduct when said other side of said capacitor isnegative relative to said terminal, and a circuit connected between theother side of said capacitor and ground for removing a positive chargefrom said other side of said capacitor, the last said circuit includinga unidirectional element polarized to conduct when said other side ofsaid capacitor tends to become positive relative to ground.

4. The combination called for in claim 3 including means including aunidirectional circuit element for preventing the potential at saidterminal from becoming negative relative to ground.

References Cited by the Examiner UNITED STATES PATENTS DAVID J. GALVIN,Primary Examiner.

ARTHUR GAUSS, Examiner.

1. IN AN INDIVIDUAL PERCUSSION KEYER CIRCUIT FOR A MUSICAL INSTRUMENTFOR USE WITH A RESPECTIVE INDIVIDUAL MUSICAL TONE SIGNAL SOURCEREPRESENTATIVE OF A SINGLE MUSICAL NOTE TO CONNECT THE RESPECTIVE SOURCETO AN OUTPUT SYSTEM COMMON TO A PLURALITY OF INDEPENDENT SUCH SOURCESUPON THE ACTUATION OF A RESPECTIVE PLAYING KEY, AN ELECTRONIC VARIABLEIMPEDANCE DEVICE THE IMPEDANCE OF WHICH IS DEPENDENT UPON THE POTENTIALAPPLIED TO A TERMINAL THEREOF, CIRCUIT MEANS INCLUDING SAID VARIABLEIMPEDANCE DEVICE FOR CONNECTING SAID SOURCE TO SAID OUTPUT SYSTEM, MEANSNORMALLY APPLYING A BIAS POTENTIAL TO SAID TERMINAL TO RENDER SAIDCIRCUIT MEANS INEFFECTIVE TO CONDUCT SAID SIGNAL TO SAID OUTPUT SYSTEM,MEANS INCLUDING THE PLAYING KEY FOR APPLYING A PULSE TO SAID VARIABLEIMPEDANCE DEVICE TERMINAL IN RESPONSE TO ACTUATION OF SAID KEY TO CHANGETHE POTENTIAL AT SAID TERMINAL SUBSTANTIALLY INSTANTANEOUSLY TO RENDERSAID CIRCUIT MEANS EFFECTIVE TO CONDUCT SAID SIGNAL TO SAID OUTPUTSYSTEM, AND AUTOMATIC MEANS OPERATIVE WITH THE APPLICATION OF SAID PULSETO REESTABLISH SAID NORMAL BIAS POTENTIAL TO SAID TERMINAL AT A SLOWRATE FOLLOWING THE APPLICATION OF SAID PULSE TO SAID TERMINAL FORPROGRESSIVELY RENDERING SAID CIRCUIT MEANS INEFFECTIVE TO CONDUCT SAIDSIGNAL TO SAID OUTPUT SYSTEM.